US President Donald Trump delivers a statement about missile strikes on a Syrian airfield, at his Mar-a-Lago estate in West Palm Beach, Florida, US, April 6, 2017. (Photo:Reuters)

Fears of confrontation between Russia and the West have been running high since Trump said on April 11 that missiles "will be coming" after the suspected chemical weapons attack in the Syrian town of Douma on April 7, and lambasted Moscow for standing by Syrian President Bashar al-Assad.

"We have proof that last week ... chemical weapons were used, at least with chlorine, and that they were used by the regime of Bashar al-Assad," Macron said, without offering details of any evidence.

"We will need to take decisions in due course, when we judge it most useful and effective," he told broadcaster TF1.

Prime Minister Theresa May prepared to convene a special cabinet meeting at 1430 GMT to weigh whether Britain should join the United States and France in a possible military action.

May recalled ministers from their Easter holiday to debate action over what she has cast as a barbaric poison gas attack in Douma, then rebel-held, just east of the capital Damascus.

There were signs, though, of a global effort to head off a direct confrontation between Russia and the West. The Kremlin said a crisis communications link with the United States, created to avoid an accidental clash over Syria, was in use.

"The situation in Syria is horrific, the use of chemical weapons is something the world has to prevent," Britain's Brexit minister David Davis said.

"But also it's a very, very delicate circumstance and we've got to make this judgment on a very careful, very deliberate, very well thought-through basis."

NAVAL MANOEUVRES

Syria's military has repositioned some air assets to avoid missile strikes, US officials told Reuters. Locating them alongside Russian military hardware might make Washington reluctant to hit them.

Russia, Assad's most important ally in his seven-year-old war with rebels, said it had deployed military police in Douma on April 12 after the town was taken over by government forces.

"They are the guarantors of law and order in the town," RIA news agency quoted Russia's defence ministry as saying.

Assad said any Western action "will contribute nothing but an increase in instability in the region, threatening international peace and security", Syrian state TV reported.

The Russian military said it had observed movements of US Navy forces in the Gulf. Any US strike would probably involve the navy, given the risk to aircraft from Russian and Syrian air defences. A US guided-missile destroyer, the USS Donald Cook, is in the Mediterranean.

Moscow's ambassador to Lebanon, Alexander Zasypkin, warned on April 11 any US missiles fired at Syria would be shot down and the launch sites targeted.

The Syrian conflict has increasingly widened the rifts between Moscow, Washington and European powers and inflamed the bitter rivalries that run across the Middle East.

Syria and its allies Russia and Iran say reports of the attack were fabricated by rebels and rescue workers in Douma and have accused the United States of seeking to use it as a pretext to attack the government.

Nervous world stock markets showed signs of recovery after Trump signalled military strikes might not be imminent.